1. Field of Invention
The present invention relates to the technical field of fluid pressure boosters, exemplified for example by a vacuum pressure booster used in a brake booster or the like, that boost an input using a fluid pressure such as vacuum pressure or air pressure, etc. to generate a boosted output. More particularly, the invention relates to the technical field of fluid pressure boosters that suppresses the generation of abnormal noise caused by flow of fluid when operation starts.
2. Description of the Prior Art
In an automobile brake system, in order to allow a large braking force to be obtained using a small pedal depression force, conventionally, fluid pressure boosters of various types have been used that boost the pedal depression force using fluid pressure to generate a large output. One example of this type of fluid pressure booster, namely, a vacuum pressure booster that boosts pedal depression force using vacuum pressure to obtain a large output, is proposed in JP-A-57-107945 (Patent Document 1).
FIG. 4 of the present application shows a cross sectional view of the vacuum pressure booster disclosed in Patent Document 1. In FIG. 4, reference numeral 1 is a vacuum pressure booster, 2 is a front shell, 3 is a rear shell, 4 is a power piston member, 5 is a diaphragm, 6 is a power piston, 7 is a constant pressure chamber that holds pressure at a constant low, vacuum pressure, 8 is a variable pressure chamber into which air, which is a fluid with a high fluid pressure, is introduced during operation from an outside air source that is a high fluid pressure source, 9 is a valve body, 10 is an input shaft, 11 is a valve plunger, 12 is an annular atmosphere valve seat that is a high pressure valve seat and that is provided in the valve plunger 11, 13 is an annular vacuum pressure valve seat that is a low pressure valve seat and that is provided in the valve body 9, 14 is a control valve body that has an annular atmosphere valve 15 that is a high pressure valve, and an annular vacuum pressure valve 16 that is a low pressure valve, the annular atmosphere valve 15 can seat on and separate away from the atmosphere valve seat 12 and the vacuum pressure valve seat 13, 17 is a control valve, 18, 19, 20 are passage holes, 21 is an output shaft, 22 is a return spring that normally urges the power piston 6 to an inoperative position direction, 23 is a reaction disk, 24 is a vacuum pressure introduction pipe, and 25 is an atmosphere introduction port.
When the vacuum pressure booster 1 is in the inoperative state, the control valve body 14 is seated on the atmosphere valve seat 12, and is slightly separated away from the vacuum pressure valve seat 13. Further, an atmosphere valve VA which is a high pressure valve is closed and a vacuum pressure valve Vv which is low pressure valve is open. In this inoperative state, the variable pressure chamber 8 is cut off from the air, and communicates with the constant pressure chamber 7, whereby vacuum pressure is introduced to the variable pressure chamber 8. Accordingly, the power piston 6 does not move.
When a brake pedal, not shown, is depressed in this inoperative state, the input shaft 10 moves forward (to the left side in FIG. 4), and the valve plunger 11 advances. Accordingly, the vacuum pressure valve 16 seats on the vacuum pressure valve seat 13 and the vacuum pressure valve Vv is closed. Following this, the atmosphere valve seat 12 separates away from the atmosphere valve 15, whereby the atmosphere valve VA is opened. As a result, the variable pressure chamber 8 is cut off from the constant pressure chamber 7, and communicates with the air. Then, the air is introduced into the variable pressure chamber 8 such that a pressure difference develops between the variable pressure chamber 8 and the constant pressure chamber 7. Accordingly, the power piston 6 advances, and the vacuum pressure booster 1 outputs via the output shaft 21. The output is transmitted to a piston of a brake master cylinder, not shown, whereby the brake master cylinder generates brake pressure.
The reaction force generated by the brake pressure of the brake master cylinder causes the output shaft 21 to abut with the valve plunger 11 via the reaction disk 23, whereby force generated by elastic deformation of the reaction disk 23 is transmitted to the brake pedal via the valve plunger 11 and the input shaft 10 as reaction force.
When an intermediate load state is reached when both the vacuum pressure valve Vv and the atmosphere valve VA are closed, the output of the vacuum pressure booster 1 is a large output obtained by boosting the pedal depression force by a determined servo ratio. Accordingly, the master cylinder generates a brake pressure that corresponds with this large output, and the brakes operate in accordance with this brake pressure. At this time, the brake force is a large brake force that is obtained by boosting the pedal depression force.
When the brake pedal is released, the input shaft 10 and the valve plunger 11 both retract (move to the right in FIG. 4), thereby opening the vacuum pressure valve Vv while the atmosphere valve VA is closed. Then, the variable pressure chamber 8 communicates with the constant pressure chamber 7, and air introduced to the variable pressure chamber 8 flows into the constant pressure chamber 7, and is then discharged from the vacuum pressure introduction pipe 24. As a result, the pressure of the variable pressure chamber 8 reduces, and the spring force of the return spring 22 causes the valve body 9, the power piston 6 and the output shaft 21 to retract to the inoperative position. In addition, the control valve 17 is placed in the inoperative state shown in the figure. In other words, the vacuum pressure booster 1 is placed in the inoperative state shown in FIG. 4.
However, in the vacuum pressure booster 1, when the driver performs a brake operation and depresses the brake pedal, and the vacuum pressure booster 1 pushes and moves the piston of the master cylinder, whereby the piston of the master cylinder starts to perform a stroke where there is loss until a determined brake pressure is generated, namely, a loss stroke. In the loss stroke region of the master cylinder, the master cylinder hardly generates any brake pressure at all, or if brake pressure is generated it is comparatively small. Accordingly, even if the output shaft 21 pushes and applies pressure to the reaction disk 23, the elastic deformation amount of the reaction disk 23 is small, and the reaction disk 23 does not abut with the valve plunger 11. As a result, in the loss stroke region of the master cylinder, no reaction force is transmitted to the brake pedal.
In this type of vacuum pressure booster 1, when the brake pedal is depressed rapidly, air is rapidly introduced to the variable pressure chamber 8, as compared to a normal brake operation is performed. However, in the loss stroke region of the master cylinder, because no reaction force is transmitted to the brake pedal, an over stroke of the power piston 6 that is rapidly introduced into the variable pressure chamber 8 occurs. As a result, an over stroke of the valve body 9 also occurs, whereby the vacuum pressure valve Vv opens and the air introduced to the variable pressure chamber 8 escapes to the constant pressure chamber 7 side via the vacuum pressure valve Vv. In addition, when the air escapes from the variable pressure chamber 8, an abnormal noise is generated.
To address this problem, JP-A-2003-127851 (Patent Document 2) proposes a vacuum pressure booster that suppresses the generation on abnormal noise by limiting the quantity of air introduced to the variable pressure chamber 8 by rapid depression of the brake pedal.
FIG. 5 shows a sectional expanded cross sectional view of a section of a control valve of the vacuum pressure booster disclosed in this Publication. Note that structural members that are the same as those in the known vacuum pressure booster shown in FIG. 4 are denoted with the same reference numerals, and a detailed description thereof is omitted.
As can be seen in FIG. 5, in the vacuum pressure booster 1 disclosed in Patent Document 2, the atmosphere valve VA of the control valve 17 is formed from a first atmosphere valve VA1 that allows and blocks communication of the variable pressure chamber 8 and the atmosphere, and a second atmosphere valve VA2 that allows and blocks communication of the variable pressure chamber 8 and the atmosphere. In addition, an orifice passage 26 is provided that normally allows communication between the first atmosphere valve VA1 and the second atmosphere valve VA2 and the atmosphere.
In this structure, the first atmosphere valve VA1 of the control valve 17 has an annular first atmosphere valve member 27 that seats on and separates away from the atmosphere valve seat 12. In addition, the second atmosphere valve VA2 of the control valve 17 has an annular second atmosphere valve member 28 that is provided to the inside of the first atmosphere valve member 27 and seats on and separates away from the atmosphere valve seat 12.
In addition, when the vacuum pressure booster 1 is inoperative, the first atmosphere valve VA1 and the second atmosphere valve VA2 are closed, and communication of the atmosphere and the orifice passage 26 and the variable pressure chamber 8 is blocked. Moreover, when the vacuum pressure booster 1 starts to operate, first, with the second atmosphere valve VA2 closed, the first atmosphere valve VA1 opens to allow communication of the variable pressure chamber 8 and the atmosphere via the orifice passage 26. As a result, air is sucked into and introduced to the variable pressure chamber 8 at a flow rate that is restricted by the orifice passage 26. Following this, the second atmosphere valve VA2 opens to allow communication of the variable pressure chamber 8 and the atmosphere via the second atmosphere valve VA2 and the first atmosphere valve VA1. As a result, the air flow rate restricting function of the orifice passage 26 is no longer effective, and the air flows without its flow rate being restricted, and is sucked into and introduced to the variable pressure chamber 8. In this manner, it is possible to suppress generation of abnormal noise caused by rapid depression of the brake pedal during the initial phase of the brake operation by first restricting the flow rate of the air that is introduced to the variable pressure chamber 8 using the orifice passage 26, and then introducing the air without restricting the flow rate.
However, in the vacuum pressure booster 1 disclosed in Patent Document 2, when the brake pedal is depressed slowly, after the first atmosphere valve VA1 has opened, only a small amount of air is taken in before the second atmosphere valve VA2 opens. As a result, air that passes through the orifice passage 26 and the gap between the first atmosphere valve member 27 of the first atmosphere valve VA1 and the atmosphere valve seat 12 generates flow noise (inflow noise).
In addition, because the flow rate restricting function of the orifice passage 26 is no longer effective, it is necessary to specially provide the first atmosphere valve member 27 in addition to the second atmosphere valve member 28 that is the originally provided atmosphere valve. As a result, the shape of the control valve body 14 is unavoidably complicated. In addition, the first atmosphere valve member 27 and the second atmosphere valve member 28 are provided on a single surface of the control valve 17, and the first and the second atmosphere valves 27, 28 seat on and separate away from the single atmosphere valve seat 12 of the valve plunger 11. Accordingly, it is comparatively difficult to set the timing from after the first atmosphere valve VA1 opens to when the second atmosphere valve VA2 opens. In addition, because the orifice passage 26 is provided in the control valve body 14 made of flexible material like rubber, there is a possibility that the cross sectional area of the orifice passage 26 will change, thereby causing the air flow rate to change. To avoid this, a reinforcement plate 29 is used to strengthen the section of the control valve body 14 that forms the orifice passage 26. As a result, the shape of the control valve body 14 is more complicated and requires more processing steps, which in turn hinders improvements in ease of manufacturing.